In the past, a production method of a casting mold has been known, which comprises the steps of filling a cavity of a heated metal mold with a resin-coated sand prepared by coating a refractory aggregate with a binder material such as thermosetting resin, and then thermally curing the binder material. According to this method, the casting mold can be produced with high productivity and stable quality. However, since it is needed to heat the metal mold at a high temperature, there is a problem that toxic substances such as ammonia gas and formaldehyde occur from a rapid reaction accompanied when the binder material such as phenol resin is cured, and consequently lead to a deterioration of working conditions.
To improve these problems, for example, Japanese Patent Early Publication No. 2000-107835 discloses a method for stably producing a casting mold within a reduced time period, while preventing the deterioration of working conditions. This method is characterized by filling the resin-coated sand in a metal mold, and then supplying superheated steam in the metal mold to instantly cure the binder material. Since heat of the superheated steam is instantly transmitted to the inside resin-coated sand, which does not contact the metal mold, the casting mold can be produced within a short time period even when the metal mold is heated at a temperature lower than before. In addition, there is an advantage of remarkably reducing the generation of toxic gas species.
However, in the case of producing the casting mold having a complex shape, since it is difficult to uniformly supply the superheated steam all over the resin-coated sand filled in a cavity of the metal mold, there is a possibility that variations in quality of the casting mold occur due to insufficient curing. In addition, when the resin-coated sand filled in the metal mold has a low void fraction, it is hard to allow the superheated steam to pass through the resin-coated sand, as compared with the case that the void fraction is high. As a result, there is another problem of preventing a uniform supply of heat into the filled resin-coated sand.